1. Technical Field
This invention generally relates to a tantalum capacitor case that increases the electrolyte volume of the standard size case, and to a method for assembling the tantalum capacitor.
2. Background Art
There are at least two common conventional tantalum electrolytic capacitor configurations. The first configuration is illustrated by FIG. 1. The capacitor assembly is contained in a case 13 having a height greater than its diameter. The case 13 contains an isolator 12, which is formed from an electrically insulative material and is shaped so that it may receive a tantalum anode 8. The isolator 12, as shown in FIG. 1, is a flat disk of insulative material that sits under the anode 8 and prevents the anode 8 from coming into contact with the case 13. The isolator 12 also comprises a ring of insulative material that fits down around the sides of the anode 8. The isolator 12 may also be arranged so that legs on the isolator 12 extend upward and allow the anode 8 to be placed inside them.
With the anode 8 in place, the case 13 is filled with electrolyte. A plug 6, which is typically formed from Teflon due to its resilience and resistance to electrolyte, has an ‘O’ ring 11 placed around it. The plug 6 and the ‘O’ ring 11 are then placed on top of the anode 8. The case 13 is then crimped around the plug 6 and the ‘O’ ring 11 with an annular crimp 10. This crimp 10 around the ‘O’ ring 11 forms a seal and prevents the electrolyte from leaking beyond the plug 6. A cap 2 is then placed on top of the case 13. The cap 2 must be aligned with the top of the case 13 in order to create a second seal over the end of the case 13. The cap 2 is then welded into place with a weld around the edge of the cap 2 from the side. The cap 2, which was constructed prior to attachment, contains a glass insulative seal 14. The seal 14 contains a lead tube 15, which allows a lead 16 from the anode 8 to extend through the cap 2. The lead tube is sealed off by a weld. An extension lead 18 formed from a metal alloy such as tin-coated copper or tin-coated nickel is then welded to the sealed lead tube 15. A second lead (not shown) is conventionally welded to the bottom of the case 13 and acts as the cathode lead.
The second conventional tantalum capacitor configuration is illustrated in FIG. 2. The capacitor is contained in a case 13 having a height less than its diameter. An isolator 50 is placed in the bottom of the case 13. This isolator 50 is simply a disk of insulative material that the anode 8 rests on. Another isolator 51 is placed around the anode 8. The bottom and side isolators 50 and 51 are conventionally formed of an electrically insulative material such as Teflon. A tantalum anode 8 is placed on the isolator 50 and the side isolator 51. The isolators 50 and 51 function to hold the anode 8 in place and prevent the anode 8 from contacting the wall of the case 13. A third isolator 52 is placed on top of the anode 8. The lid 2 is secured to the case 13 and then the case 13 is filled with electrolyte 54. The lid 2 fits down inside the case 13, pressing firmly against the second isolator. The broad support provided by the cap 2 against the top isolator 52 provides substantially even support on the anode 8. A weld is then run along the edge of the case 13 and the cap 2. The cap 2 also contains an insulative glass seal 14. This seal 14 contains a lead tube 15, which allows a lead 16 to be passed from the anode 8 to the inside of the tube 15.
In the tantalum capacitor field there are several known conventional methods of filling capacitors of the type shown in FIG. 2 with electrolyte. One method is to utilize a vacuum to draw the electrolyte into the capacitor after the cap 2 is in place. After the capacitor is sealed with the cap 2, it is placed in a tub of electrolyte under vacuum. The vacuum forces the air out of the capacitor. When the vacuum is removed, the electrolyte flows into the case 13 through the lead tube 16, which is the only opening in to the capacitor. The lead tube 16 is then sealed with a weld. The capacitor may also be filled with electrolyte through an additional orifice designed to receive electrolyte. The orifice is then welded shut.
Electrolyte is consumed slowly over the life of a traditional electrolytic tantalum capacitor. Therefore, the more electrolyte that is available for use in the case, the longer the life of the capacitor will be. In the traditional capacitors, the cap or the combination of the cap and plug take up room inside the case, thereby reducing the amount of room available for electrolyte in the case.